Implantable devices for pacing, cardioversion, defibrillation and resynchronization of cardiac electrical and mechanical function are widely available to prevent and treat symptomatic bradyarrhythmias, tachyarrhythmias and dysynchronous myocardial mechanics. Impaired cardiac performance can result from several abnormalities. Such abnormalities include alterations in the normal electrical conduction patterns and mechanical abnormalities in myocardial contractility. These abnormalities are often (though not necessarily) connected to one another and, as such, electromechanical impairments can cause an impairment in cardiac performance as well. Such impairment in cardiac performance often stems from premature or delayed electrical and/or mechanical events in different cardiac chambers and within specific cardiac chambers. For example, conduction abnormalities may occur between the atria and the ventricular chambers, which are known as atrial-ventricular dysynchrony. Abnormalities between right and left ventricular chambers (inter-ventricular) or within the right or left ventricles (intra-ventricular) can result in dysynchrony as well. Dysynchrony leads to ineffective work as a result of forces being generated in specific regions at inappropriate times relative to the opening and closing of the heart valves. It can lead to myocardial relaxation during times where the generation of force in all myocardial segments should be occurring synchronously and in a symmetric fashion in relation to valvular events and myocardial thickening when all myocardial segments should be relaxing, diastole, and receiving oxygenated blood from the lungs. Multiple variations in the location and pattern of dysynchrony may exist in individual patients.
Methodologies exist for optimizing the timing of pacing impulses in such systems including extrinsic measurements using echocardiography and intrinsic methodologies described by the inventor and others. Intrinsic or closed loop systems for monitoring purposes and optimizing interval timing within such implanted devices are in development.
These systems may employ measurements of cardiac performance and indices of dysynchrony. Several methodologies have been proposed including pressure transducers, oxygen saturation sensors, ultrasonic dimension sensors, accelerometers, measurements of electrical activation patterns and impedance based measurements. Such technologies may require large lead bodies, multiple transducers and can place significant energy demands secondary to signal processing. The present disclosure employs an acoustic sensor, such as a sonomicrometer, that detects intrinsic cardiac sound and characterizes a wide range of acoustic properties including but not limited to intensity, frequency, duration and self-similarity. The system then relates this acoustic data to other sensed signals, such as intracardiac electrograms and impedance waveforms, to optimize timing of pacing impulses and to provide data for monitoring and diagnostic purposes.
References that relate to the present disclosure include the following U.S. patents and published patent applications, each of which is incorporated herein by reference: U.S. Pat. No. 6,804,559, “Electromedical Implant,” issued Oct. 12, 2004 to Kraus et al.; U.S. Pat. No. 6,795,732, “Implantable Medical Device Employing Sonomicrometer Output Signals for Detection and Measurement of Cardiac Mechanical Function,” issued Sep. 21, 2004 to Stadler et al.; U.S. Pat. No. 6,792,308, “Myocardial Performance Assessment,” issued Sep. 14, 2004 to Corbucci; U.S. Pat. No. 6,816,301, “Micro-electromechanical Devices and Methods of Manufacture,” issued Nov. 9, 2004 to Schiller; U.S. Pat. No. 6,572,560, “Multi-Modal Cardiac Diagnostic Decision Support System and Method,” issued Jun. 3, 2003; U.S. published patent application number 20040176810A1, “Implantable Medical Device Employing Sonomicrometer Output Signals for Detection and Measurement of Cardiac Mechanical Function,” published Sep. 9, 2004 to Stadler et al.; and U.S. published patent application number 20030083702, “Implantable Medical Device Employing Sonomicrometer Output Signals for Detection and Measurement of Cardiac Mechanical Function,” published May 1, 2003 to Stadler et al.